Continuous flow endoscopes are frequently used in endoscopic procedures such as hysteroscopy, trans uretheral urologic endoscopic procedures and arthroscopy. Those skilled in the art would know the structural composition of a continuous flow irrigation endoscope. In this application, the term “continuous flow irrigation” means that fluid simultaneously enters and escapes from a tissue cavity via separate entry and exit points, as a result of which positive fluid pressure is created inside the tissue cavity which distends the cavity.
A typical continuous flow irrigation endoscope comprises an inner sheath which is placed inside the cylindrical lumen of an outer sheath. The sheaths are hollow cylindrical tubes which have a distal end which enters a tissue cavity and a proximal end on which an inflow or outflow port is attached for the purpose of instilling or evacuating fluid from the cavity. The irrigation fluid is instilled via an inflow port. In many prior art systems, the instilled fluid travels through the lumen of the inflow sheath and enters the tissue cavity via the distal opening of the inflow sheath. The waste fluid present inside the tissue cavity enters into a potential space present between the outer and the inner sheaths via multiple holes present near the distal end of the outer sheath and this waste fluid is finally evacuated via the outflow port attached at the proximal end of the outer sheath. A fiber optic telescope is placed inside the cylindrical lumen of the inner sheath in order to view the interior of the tissue cavity. An endoscopic instrument, such as a wire loop electrosurgical cutting loop, is also placea in the lumen of the inner sheath. The positions of the outer sheath, the inner sheath and the telescope remain fixed with respect to each other. However, the electrosurgical cutting loop is capable of moving in a to and fro direction by virtue of which prostate tissue and uterine endometrial tissue is resected. The to and fro movement of the cutting loop is made by attaching the same to an externally located resectoscope.
In the arrangement described in the preceding paragraph, detached tissue pieces, larger than a critical size, present in the tissue cavity are unable to pass through the potential space between the outer and the inner sheaths. Thus, in endoscopic procedures such as endometrial resection and prostate resection, the entire endoscope or the “endoscopic instrument” has to be intermittently removed from the tissue cavity during the surgery to evacuate the detached tissue pieces present inside the tissue cavity, and this increases the risk of complications like perforation, excessive bleeding and also increases the surgical time. Let it be assumed that the positions of the inflow and outflow port are reversed which implies that the inflow port would be attached to the outer sheath while the outflow port would be attached to the inner sheath. Let it be further assumed that the inner lumen diameter of the outflow port is equal to the lumen diameter of the inner sheath. It could be argued that, in such an arrangement, detached tissue pieces and waste fluid would both be easily evacuated through the wide inner sheath and through the wide bore outflow port. However, such an arrangement could also cause the pressurized irrigation fluid present inside the tissue cavity to be expelled via the wide bore outflow port. This, in turn, could cause the tissue cavity to intermittently collapse during a surgical procedure, which in turn could lead to complications such as perforation and bleeding. It is for these reasons that the lumen diameter of the outflow port, in the prior art systems, is kept as less as possible. The system of the proposed invention solves the problems described in this paragraph despite the outflow port having a relatively large lumen diameter.